Manufacture of open-hearth steel.



ANSON W. ALLEN, OF PHILADELPHIA, PENNSYLVANIA.

MANUFACTURE OF OPEN-HEARTH STEEL.

Specification of Letters Patent.

Patented Nov. 12, 1907.

Application filed April 3. 1906. Serial No. 309.726.

To all whom it may concern:

Be it known that'I, ANsoN W. ALLEN, of Philadelphia, in the county ofPhiladelphia and State of Pennsylvania, have invented an Improvement inthe Manufacture of Open-Hearth Steel, of which the following is aspecification.

I have discovered that important improvements in the manufacture ofopen-hearth steel can be obtained by charging in a basic linedopen-hearth furnace a charge of iron oxid and burnt lime, heating thesame, and then pouring upon the heated charge of lime and iron oxid acharge of molten metal. When this is done a reaction immediately ensues,in which the phosphorus and silicon of the iron are caused to combinewith the iron oxid and lime, forming a molten slag, so that the ironrapidly becomes dephosphorized and desiliconized. This reaction is notviolent and does not cause the overflow of the slag from the furnace,but the slag containing the phosphorus and siliconis allowed to remain,either in whole or in major part, as a floating body upon the surface ofthe iron. This can be done without important delay to the operation ofthe furnace, because the slag being produced without violent reaction,is dense in its nature and is not foamy, as the slag which is producedby reaction with unburnt limestone and iron oxid, and therefore does notinterfere with the transmission of the heat from the furnace to the ironbelow. The advantage of thus leaving the slag, or the bulk of it,remaining in the furnace is that a very large saving of iron is effectedthereby. If the slag is immediately tapped off after a violent reaction,a large part of the iron oxid passes with it; but by allowing it toremain in the furnace, the iron oxid contained in the slag reacts withthe charge of molten iron, decarbonizing the same and giving up the ironof the slag to the bath, so that when the slag is eventually tapped fromthe furnace it is lean in iron and therefore is not the cause of waste.

In the practice of my invention I may introduce scrap into the furnaceas part of the original charge to the extent of one-third of the totalmetal charge, though an important advantage of my invention is that itenables me to conduct the open-hearth operation without the use ofscrap. I may also, in the practice of the invention, withdraw a part ofthe slag from the furnace after the initial reaction caused by theintroduction of the molten iron, though I deem it desirable, as abovestated, that all of the slag should be allowed to remain in the furnace,and it is essential to my invention that a considerable part of the slagproduced by the reaction be thus allowed to remain.

To inform those skilled in the art as to the preferable practice of theinvention, I will now proceed to describe an open-hearth heat in whichthe invention was carried out. In this heat I introduced on the bottomof the furnace a charge of scrap steel and placed upon it iron oxid inthe form of mill scale amounting to about 20 per cent. of the metalcharge of the furnace, and burnt lime amounting to about 4% per cent.thereof. 1 then placed scrap on top of the lime and oxid, the totalamount of scrap equaling about 20 per cent. of the metal charge of thefurnace. I then heated these materials for a period of one hour andone-half, the heat being preferably continued until the iron oxid beganto sweat or show signs of incipient fusion, but the length of thepreheating period may be varied as desired.

The purpose of preheating the oxid to a considerable extent is to renderthe reaction more efficient, for unless the iron oxid is heated to astate approaching sweating or incipient fusion the desired reaction willnot be obtained. The order of introducing the iron oxid and lime andscrap relatively to each other may be changed. I then added to thefurnace molten metal, introducing it in two lots at an interval of 35minutes apart, each portion introduced amounting to 26,850 pounds andcontaining approximately 3.8 per cent. of carbon and .8 per cent.phosphorus. At the introduction of the first lot of molten iron to thefurnace a reaction took place which was quiet in its nature and notviolent, and which produced a rapid elimination of the phosphorus fromthe metal, so that in 5' minutes the phosphorus was reduced to .612 percent.; in 10 minutes it was reduced to .396 per cent.; in 15 minutes, to.288 per cent.; and in 20 minutes to .070 per cent. On the introductionof the second ladle of iron,which was made 35 minutes after the pouringof the first ladle, a supplemental reaction ensued, and in 5 minutesthereafter the charge in the furnace contained .392 per cent.phosphorus; in 10 minutes it contained .268 per cent. phosphorus; in 15minutes it contained .224 per cent.; in 25 minutes, .097 per cent.phorphorus, and in 45 minutes .016 per cent. phosphorus.

The carbon was eliminated from the metal more slowly, and the entireheat lasted 4 hours and 55 minutes. The total metal output of thisfurnace was 72,390 pounds, or 6,520 pounds more than was charged intothe furnace in the form of metallic iron, the addition being obtainedfrom reduction offthe iron ore.

The slag was tapped from the furnace at the end of theticular operationdescribed therein, but that many variations may be made from the saidoperation with out departing from the scope of my invention.

The advantages of the invention are due to the fact that I am enabled,without the use of the large scrap charge ordinarily employed in the pigand scrap process, which amounts approximately to 50 per cent or more ofscrap, to produce basic open-hearth steel rapidly and with a minimum oflabor and with a minimum of waste of iron, the essentials of theinvention being the use of burnt lime as part of the initial heatedcharge of the furnace, and the retaining oi the slag or the bulk of theslag in the furnace after the initial reaction takes place, in orderthat the iron of the slag may not be lost.

If desired, mill cinder or iron ore may be substituted in whole or inpart for the roll scale as the iron oxid to be employed in the reaction.

Those skilled in the art will be able to modify the process in variousways without departure from the invention as stated in the claims, sinceWhat I claim is:

1. The method herein described of making open hearth steel whichconsists in introducing into a basic open hearth furnace iron oxid andburnt lime, heating the same to a state approaching incipient fusion,then introducing the molten pig iron containing phosphorus and retainingon the bath the bulk of the slag until the final stages of the heat,thus obtaining a reaction which eliminates the phosphorus from the iron.

2. The herein described method of making open-hearth steel, whichconsists in introducing iron oxid and burnt lime to the bottom of abasic open-hearth furnace, heating the furnace until the iron oxidbegins to sweat or Show signs of incipient fusion, then pouring moltenpig iron containing phosphorus upon the surface of the initial charge toobtain a reaction for eliminating the phosphorus from the iron, and forretaining the slag or the bulk thereof on the surface of the bath untilthe final stage of the heat to permit the slag to give up its iron tothe bath. I

In testimony whereof, I have hereunto set my hand.

ANSON W. ALLEN.

Witnesses THOMAS W. BAKEWELL, J. H. GRAY.

